NLR signaling in plants: from resistosomes to second messengers.

Nucleotide binding and leucine-rich repeat-containing receptors (NLRs) have a critical role in plant immunity through direct or indirect recognition of pathogen effectors. Recent studies have demonstrated that such recognition induces formation of large protein complexes called resistosomes to mediate NLR immune signaling. Some NLR resistosomes activate Ca influx by acting as Ca-permeable channels, whereas others function as active NADases to catalyze the production of nucleotide-derived second messengers. In this review we summarize these studies on pathogen effector-induced assembly of NLR resistosomes and resistosome-mediated production of the second messengers of Ca and nucleotide derivatives. We also discuss downstream events and regulation of resistosome signaling.